The invention pertains to a process of removing contaminants from olefin feedstocks using a sorbent comprising a metal. The contaminants removed preferably are phosphorus-containing compounds, most preferably organophosphines and/or organophosphine oxides. Preferred olefin feedstocks are made by oligomerizing ethylene to linear olefins having from about 6 to about 36 carbon atoms, preferably from about 11 to about 20 carbon atoms, and most preferably from about 14 to about 18 carbon atoms.
Depending upon the method of their production, olefin feedstocks may comprise a variety of impurities. Impurities found in olefins that are produced by oligomerization of ethylene units include phosphorus-containing impurities, including but not necessarily limited to organophosphines and organophosphine oxides. These phosphorus-containing compounds are largely removed from many olefin streams during the process of distillation to separate various xe2x80x9ccutsxe2x80x9d of olefins. Unfortunately, the organophosphines and organophosphine oxides found in C14-C18 streams tend to co-distill with the C14-C18 in the product, making it difficult, if not impossible to remove these phosphine impurities by simple distillation.
C6-C36 olefins have utility in the fields of paper and pulp processing, drilling fluids, and machine or metal working oils. Alcohols of such olefins have commercial importance in a variety of applications, including detergents, soaps, surfactants, and freeze point depressants in lubricating oils. These alcohols are produced by a number of commercial processes, such as by oxo or hydroformylation of long chain olefins. In many of these applications, the olefin feedstocks are treated using acid catalysts.
Unfortunately, any phosphorus-containing compounds in these olefin feedstocks will negatively affect acid catalysts. The phosphorus-containing moieties are basic in nature and will neutralize the active acid sites of the catalyst, which lowers catalyst activity and performance. The organophosphine moeities may even cause the olefins to oligomerize into undesirable forms.
Methods are needed to reduce the phosphorus-content of olefin feedstocks.
The present invention provides a method for purifying an olefin feed comprising a content of phosphorus-containing compounds. The method comprises contacting the olefin feed with a sorbent comprising a metal under conditions and for a time effective to reduce the content of phosphorus-containing compounds, producing a purified olefin feed.
The present invention provides a process and sorbents which efficiently and effectively reduce the content of phosphorus-containing compounds in olefin streams. In a preferred embodiment, the content is reduced to about 1 ppm or less, preferably about 0.5 ppm or less, most preferably to about 0.1 ppm or less. Given sufficient run time, the sorbents reduce the content of phosphorus-containing compounds in the olefin stream to parts per billion (ppb) levels.
The invention may be used to treat substantially any olefin stream. Preferred olefin streams are linear olefin streams made by oligomerizing ethylene. Some of the known processes for oligomerizing ethylene use organophosphorus compounds that result in phosphorus as a contaminant in the resulting olefin stream. A preferred commercially available olefin feed for the treatment of the present invention is the product marketed in the United States by Shell Chemical Company under the trademark NEODENE(copyright). In a preferred embodiment, the olefin feedstock is treated before exposure to an acid catalyst, or before exposure to other conditions which would be adversely affected by the basic nature of phosphorus-containing contaminants.
In a most preferred embodiment, the olefin stream is the feedstock for the skeletal isomerization catalyst used in the method described in U.S. Pat. No. 5,849,960, which has been incorporated herein by reference. The olefins used in the feed to this skeletal isomerization catalyst are mono-olefins having at least 6 carbon atoms, preferably having from about 11 to about 20 carbon atoms, and most preferably having from about 14 to about 18 carbon atoms.
In general, the olefins in the feed to the skeletal isomerization catalyst are predominately linear. While the olefin feed can contain some branched olefins, the olefin feed processed for skeletal isomerization preferably contains greater than about 50 percent, more preferably greater than about 70 percent, and most preferably greater than about 80 mole percent or more of linear olefin molecules.
The olefin feed to the skeletal isomerization catalyst does not consist of 100% olefins, and usually contains a distribution of mono-olefins having different carbon lengths, with at least 50 wt. % of the olefins being within the stated carbon chain range or digit, however specified. Preferably, the olefin feed will contain greater than 70 wt. %, more preferably about 80 wt. % or more of mono-olefins in a specified carbon number range, the remainder of the product being olefins of other carbon number or carbon structure, diolefins, paraffins, aromatics, and other impurities resulting from the synthesis process. The location of the double bond is not limited. The olefin feed composition may comprise alpha olefins, internal olefins, or a mixture thereof.
The sorbent of the present invention comprises a suitable metal, preferably comprising metal oxide, on a suitable support. Preferred metals are transition metals, including but not necessarily limited to those selected from Groups 3-12 of the Periodic Table of the Elements. When the Periodic Table of the Elements is referred to herein, the source of the Periodic Table is: F. Cotton et al. Advanced Inorganic Chemistry (5th Ed. 1988). Suitable metals include, but are not necessarily limited to Sc, V, Cr, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mn, Ag and combinations thereof. Preferred metals are Fe, Co, Ni, Mn, Ag and Cu. In a preferred embodiment, the metal is silver or copper, preferably in the form of oxides. The sorbent suitably comprises from about 0.1 wt. % to about 50 wt. % of the metal oxide of the foregoing metals, preferably copper. Preferably, the sorbent comprises from about 1 wt. % to about 20 wt. %, more preferably from about 5 wt. % to about 15 wt. %, and most preferably from about 8 wt. % to about 10 wt. % of the metal oxide.
The metal oxide resides on a suitable support material. Although the surface area of the support is not a critical feature, the surface area preferably is at least about 10 m2/g in order to provide sufficient contact between the sorbent and the olefin stream. In a preferred embodiment, the support has a surface area of from about 100 m2/g to about 900 m2/g. Acidic supports are more advantageous than basic supports. Suitable support materials are acidic or neutral, most preferably acidic. Suitable support materials include, but are not necessarily limited to alumina, silica, molecular sieves, such as zeolites, activated carbon, aluminosilicate clays, amorphous silicoaluminas, and the like. Where the support material surface is porous, the pores preferably are sufficiently large to permit entry of bulky phosphorus containing compounds in the feed. A most preferred support material for copper is an acidic or neutral alumina. A most preferred support material for silver is X-zeolite. A commercially available sorbent that is suitable for use in the present invention is SELEXSORB AS(trademark), which is commercially available from Alcoa Industrial Chemicals.
It is preferred for the particles of supported sorbent to be as small as possible; however, if the size of the particles is too small, the pressure drop through the bed becomes too large. Very small particles also are difficult to retain in the sorbent bed. SELEXSORB AS(trademark) is purchased in the form of xe2x85x9 inch spheres, and may be used in the process as purchased. However, spheres are not the most efficient particle shape for purposes of maximizing particle surface to volume ratio. Because of this, if SELEXSORB AS(trademark) is used as the sorbent, it is preferred to grind or otherwise reduce the xe2x85x9 inch spheres into the smallest particles possible without inducing an undue pressure drop or loss of sorbent from the sorbent bed. The particles may have substantially any form, including but not necessarily limited to spherical form, tablet form, cylindrical form, multi-lobed cylindrical forms, and their corresponding hollow counterparts. In a preferred embodiment, the particles have a diameter of from about 50 mesh to about 6 mm, preferably about 0.8 mm ({fraction (1/32)} inch) to about 1.6 mm ({fraction (1/16)} inch), most preferably about 0.8 mm. The length of the particles is not critical, with suitable lengths including, but not necessarily limited to less than about 10 mm, preferably from about 3 mm to about 5 mm.
In a preferred embodiment, the support material is an alumina extrudate which is extruded as a paste using an acidic or neutral alumina powder. The xe2x80x9cpastexe2x80x9d is extruded or otherwise molded into a multilobed cylindrical form. The resulting material preferably is dried at temperatures of at least about 100xc2x0 C. and calcined at about 500xc2x0 C. or more in the presence of flowing air in a muffle furnace or purged high temperature air drier or rotary calciner. The copper oxide may be deposited onto the support using any suitable technique, including but not necessarily limited to ion exchange, co-mulling, or impregnation. A preferred technique is pore volume impregnation using a solution of a copper salt, such as copper nitrate, copper carbonate, or other suitable salts. Although the following illustration uses a copper nitrate solution, the use of other Cu salt solutions may produce a more uniform Cu loading. Copper nitrate is very soluble in water, and tends to wick out of the pores during drying. The result may be more CuO on the outside of the pellets, although smaller pellets are less prone to this effect.
Persons of ordinary skill in the art have the knowledge required to calculate how to incorporate a given wt % of CuO or other material onto a sorbent using the foregoing techniques. For example, where 100 g of an alumina has a water pore volume of 83 ml, the following is a formula by which a sorbent containing 9 wt. % CuO is formed:   [            (              9        ⁢                  xe2x80x83                ⁢                              g            .                          xe2x80x83                        ⁢            CuO                    /          100                ⁢                  xe2x80x83                ⁢                  g          .                      xe2x80x83                    ⁢          final                ⁢                  xe2x80x83                ⁢        sorbent            )        xc3x97          (              1        ⁢                  xe2x80x83                ⁢        mole        ⁢                  xe2x80x83                ⁢                  CuO          /          79.54                ⁢                  xe2x80x83                ⁢                  g          .                    )        xc3x97          xe2x80x83        ⁢          [              1        ⁢                  xe2x80x83                ⁢        mole        ⁢                  xe2x80x83                ⁢        Cu        ⁢                  xe2x80x83                ⁢                                            (                              NO                3                            )                        2                    ·          2.5                ⁢                  xe2x80x83                ⁢                  H          2                ⁢                  O          /          mole                ⁢                  xe2x80x83                ⁢        CuO            ]        xc3x97          (              232.59        ⁢                  xe2x80x83                ⁢                  g          .                      xe2x80x83                    ⁢          Cu                ⁢                  xe2x80x83                ⁢                                            (                              NO                3                            )                        2                    ·          2.5                ⁢                  xe2x80x83                ⁢                  H          2                ⁢                  O          /          mole                ⁢                  xe2x80x83                ⁢        Cu        ⁢                  xe2x80x83                ⁢                                            (                              NO                3                            )                        2                    ·          2.5                ⁢                  xe2x80x83                ⁢                  H          2                ⁢        O            )        ]
In other words, it requires 0.26 g. Cu(NO3)2.2.5 H2O per g., of final sorbent to form a 9 wt. % CuO on alumina sorbent where the water pore volume is 83 ml of water per 100 g. of copper oxide on alumina.
In order to prepare the 9 wt. % CuO on alumina, the pores of 91 g. of the alumina are filled with a solution containing 26 g. (0.26 g. of Cu(NO3)2.2.5 H2O/g. sorbentxc3x97100 g.) copper nitrate salt dissolved in 75.5 ml. of water to incipient wetness. Slightly more or less liquid solution may be added until the catalyst is uniformly filled with solution. In the case of Cu salts, the color of the filled pellets is light blue and the unfilled pellets remain white. The sorbent is dried in an oven at a temperature sufficient to boil water from the pores without fracturing the sorbentxe2x80x94about 121xc2x0 C. (250xc2x0 F.)xe2x80x94for from about 4 to about 8 hours. Then, the temperature is ramped to about 482xc2x0 C. (900xc2x0 F.) to decompose the nitrate salt to CuO on the support. Prior to use, the sorbent is stripped with nitrogen in order to avoid contaminating the olefin feed with oxygen.
Preferably, the olefin feedstock is contacted in the liquid phase in a reaction zone with the sorbent of the present invention at effective process conditions to reduce the content of phosphorus-containing compounds in the feedstock, i.e., an effective temperature, pressure, and LHSV (Liquid Hourly Space Velocity). A preferred embodiment of a reactor system for the process is an upflow or downflow fixed bed reactor. An upflow reactor is preferred for better wetting of the sorbent bed. The temperature employed may vary. Although not limited to a particular temperature, best results will be obtained if the process is conducted at temperatures of from about 0xc2x0 C. to about 100xc2x0 C., preferably from about 10xc2x0 C. to about 50xc2x0 C. The pressures may vary over a range including but not limited to autogeneous pressures and pressures in the range of from about 0.01 MPa to about 50 MPa. A preferred pressure is in the range of from about 0.1 MPa to about 10 MPa. Pressures outside of the stated ranges may be used and are not excluded from the scope of the invention.
The feedstock may flow at a wide range of liquid hourly space velocities (LHSV), defined as liquid feed per hour per volume of sorbent. The LHSV is calculated as follows:             Volume of olefin containing feed              Volume of sorbent        xc3x97      1    hr  
The lower the LHSV, the greater will be the reduction in content of phosphorus-containing compounds in the feedstock. The LHSV generally is from about 0.01 hrxe2x88x921 to about 10 hrxe2x88x921, preferably from about 0.1 hrxe2x88x921 to about 1 hrxe2x88x921.
The process is continued for a period of time sufficient to achieve a desired reduction in the content of phosphorus-containing compounds in the olefin stream. The content of phosphorus-containing compounds preferably is reduced to about 1 ppm or less, most preferably to about 0.1 ppm or less. The reaction cycle time may vary from tenths of seconds to a number of hours. The reaction cycle time is largely determined by the reaction temperature, the pressure, the sorbent selected, the liquid hourly space velocity, and the desired reduction in content of phosphorus containing compounds.
At some point, the sorbent becomes saturated, and must be regenerated. SELEXSORB AS(trademark) has an absorptive capacity of about 0.6 grams of phosphorus per gram of sorbent. The sorbent may be regenerated by exposing the sorbent to an oxygen-containing atmosphere at a temperature of from about 200xc2x0 C. to about 550xc2x0 C., preferably from about 450xc2x0 C. to about 600xc2x0 C. Suitable oxygen containing atmospheres include, but are not necessarily limited to air, oxygen gas, and a combination of oxygen gas with nitrogen gas. A preferred gas is a commercially available combination comprising about 1% oxygen, with the remainder being nitrogen. After exposure to these increased temperatures for a period of time of from about 0.5 hour to about 100 hours, the bed is cooled to at least about 100xc2x0 C., and preferably to about 25xc2x0 C., or ambient temperature, in order to avoid overheating upon reuse. The cooled bed is purged with nitrogen or air before reuse in the process. Ten regeneration cycles under these conditions have been shown to produce no loss in sorbent capacity. Some slight loss in sorbent capacity was seen beginning after about 10 regeneration cycles.
Typical olefin feedstocks comprise from about 100 ppm to about 2000 ppm dienes that tend to lower the efficiency of skeletal isomerization catalysts. In a preferred embodiment, the support of the present invention, preferably is a sorbent which sorbs dienes present in initial olefin streams. In a preferred embodiment, the alumina support for copper oxide performs this function. The dienes are sorbed onto the alumina prior to skeletal isomerization. The dienes also may be removed by sorption from the skeletally isomerized product.
C6 to C33 olefins have a variety of uses, including but not necessarily limited to uses in paper processing, drilling fluids, and machine or metal working. In a preferred embodiment, the olefin feedstock is converted to branched primary alcohols in the process described in U.S. Pat. No. 5,849,960, incorporated herein by reference. Most preferably, the olefin feedstock is treated before the olefins are fed to a skeletal isomerization catalyst, as described in U.S. Pat. No. 5,849,960. A preferred skeletal isomerization catalyst for use in conjunction with the present invention is a hydrogen ferrierite catalyst, as described in U.S. Pat. No. 5,510,306, incorporated herein by reference.
In a preferred embodiment, the skeletally isomerized olefins are converted to any of a broad range of surfactants, including nonionic, anionic, cationic, and amphoteric surfactants, with a degree of branching of at least 1.0. The skeletally isomerized olefins serve as a surfactant intermediate. Specifically, the skeletally isomerized olefins serve as the hydrophobic moiety of the surfactant molecule, while the moiety added to the olefin during the conversion process serves as the hydrophile.